I have to concur with other posters, the black market created by outlawing cigarettes would be huge. Most states have already raised the tobacco tax to near-prohibitive levels, with little corresponding decrease in smoking. I can forsee street corners dealers selling cigarettes, and students sneaking nicotine patches into school.
I agree with #3, doing something about junk food would improve people's health more. We have all sorts of campaigns to raise awareness about cancer and so on, to the point that few people realize that heart disease is actually our number-one killer; yet you never see anyone handing out ribbons saying "skip the fries".
I think that Kikie needs to realize that even asking the question is a bit idealistic. It's all about money. Our country was developed based on a free-market economy. The FDA isn't even allowed to enter onto the property of a tobacco farm without advance written permission.